The present invention relates to volume and tone control circuits for use in acoustic reproduction (audio) sets, wherein an output signal will not get distorted when the volume is adjusted to its maximum independent of the adjustment of the tone control.
One channel of a conventional volume and tone control circuit for an audio device is illustrated in FIG. 13. The variable resistor 109 is used to adjust the volume or amplitude of the audio signal appearing at input terminal 108 and fed to the tone control circuit 110. The tone control circuit is used to adjust the amplitude-versus-frequency characteristics of the signal. The adjusted signal appears at the output terminal 111. If the tone control 110 is adjusted to provide a flat response or uniform gain across the band of audio frequencies, the amplitude of the signal appearing at the output terminal 111 will be maximum or loudest when the volume control 109 is adjusted to the maximum.
The volume and tone control circuit shown in FIG. 13 is not without problems in that adjusting the volume control to its maximum may result in a distorted signal.
For example, if a listener desires to amplify or raise the bass (low frequency sound portion of the signal), the tone control is adjusted to boost the bass and attenuate the treble (high frequency sound portion of the signal) or just boost the bass portion of the signal. Then if the volume is adjusted to increase the volume or amplitude of the signal, the signal may become distorted because increasing the volume may clip the amplitude of the low frequency (bass) portion of the signal that was raised by the tone control. It should be apparent that if the tone control 110 is adjusted to flat or level gain and the volume control is not adjusted to its maximum, there is less likelihood that the amplitude of the signal will be high enough to be clipped. Of course, by keeping the low range of frequencies below their maximum level and the volume control below its maximum level, the high range of frequencies will operate below the maximum level.
Another problem with the volume and tone control circuit shown in FIG. 13 arises when a listener desires to attenuate or lower the level of the low range of frequencies. If the tone control 110 is adjusted to attenuate the bass level, then adjusting the volume control 109 to its maximum will provide a signal that is below the maximum level attainable.
The same problems described above are also applicable to the situations when the listener wants to adjust the treble or high frequency sound band to its maximum or to attenuate the treble and then adjust the volume control.
In particular, if a listener increases the bass and/or treble to a maximum level, then an adjustment of the volume control to its maximum level may clip the signal and result in a distorted signal. On the other hand, if the bass and/or treble are attenuated, then a maximum signal is not achievable by adjusting the volume control to its maximum, since the signal has been attenuated by the tone control.